Retain direction for empty KeysetScrollPosition.

We now retain the direction when an empty KeysetScrollPosition is created.

Closes #2840

Author: mp911de

src/main/java/org/springframework/data/domain/KeysetScrollPosition.java

@@ -34,9 +34,12 @@
  */
 public final class KeysetScrollPosition implements ScrollPosition {
 
-	private static final KeysetScrollPosition INITIAL = new KeysetScrollPosition(Collections.emptyMap(),
+	private static final KeysetScrollPosition EMPTY_FORWARD = new KeysetScrollPosition(Collections.emptyMap(),
 			Direction.FORWARD);
 
+	private static final KeysetScrollPosition EMPTY_BACKWARD = new KeysetScrollPosition(Collections.emptyMap(),
+			Direction.BACKWARD);
+
 	private final Map<String, Object> keys;
 	private final Direction direction;
 
@@ -55,7 +58,7 @@ private KeysetScrollPosition(Map<String, Object> keys, Direction direction) {
 	 * @return will never be {@literal null}.
 	 */
 	static KeysetScrollPosition initial() {
-		return INITIAL;
+		return EMPTY_FORWARD;
 	}
 
 	/**
@@ -70,8 +73,7 @@ static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
 		Assert.notNull(keys, "Keys must not be null");
 		Assert.notNull(direction, "Direction must not be null");
 
-		return keys.isEmpty()
-				? initial()
+		return keys.isEmpty() ? (direction == Direction.FORWARD ? EMPTY_FORWARD : EMPTY_BACKWARD)
 				: new KeysetScrollPosition(Collections.unmodifiableMap(new LinkedHashMap<>(keys)), direction);
 	}
 

src/test/java/org/springframework/data/domain/ScrollPositionUnitTests.java

@@ -129,12 +129,24 @@ void initialOffsetPosition() {
 		assertThat(position.getOffset()).isEqualTo(0);
 	}
 
-	@Test // GH-2824
+	@Test // GH-2824, GH-2840
 	void initialKeysetPosition() {
 
 		KeysetScrollPosition keyset = ScrollPosition.keyset();
 
 		assertThat(keyset.isInitial()).isTrue();
 		assertThat(keyset.scrollsForward()).isTrue();
+
+		keyset = ScrollPosition.of(Collections.emptyMap(), Direction.FORWARD);
+
+		assertThat(keyset.isInitial()).isTrue();
+		assertThat(keyset.scrollsForward()).isTrue();
+		assertThat(keyset.scrollsBackward()).isFalse();
+
+		keyset = ScrollPosition.of(Collections.emptyMap(), Direction.BACKWARD);
+
+		assertThat(keyset.isInitial()).isTrue();
+		assertThat(keyset.scrollsForward()).isFalse();
+		assertThat(keyset.scrollsBackward()).isTrue();
 	}
 }